The topside has two places to put advertisements.
The ideal size for each is:
-Width of 44" (112cm)
-Height of 22" (56cm)
-Grommets in each corner
You shouldn't go bigger. You can go smaller.
We have had good luck with https://www.esigns.com/mesh-banners/. You can use coupon esigns-club to get 10% off. Make sure to tell them you want stainless grommets in each corner. You can order their 2' x 4' banner and ask them to cut it smaller. It is right around $35 before the coupon or quantity discounts.
Below are some examples of the max size:
Here is an idea of the total size of the bot: